Presbyopia is a gradual loss of accommodation of the visual system of the human eye. This is due to an increase in the modulus of elasticity and growth of the crystalline lens of the eye that is located just behind the iris and the pupil. Tiny muscles in the eye called ciliary muscles pull and push the crystalline lens, thereby causing the curvature of the crystalline lens to adjust. This adjustment of the curvature of the crystalline lens results in an adjustment of the eye's focal power to bring objects into focus. As individuals age, the crystalline lens of the eye becomes less flexible and elastic, and, to a lesser extent, the ciliary muscles become less powerful. These changes result in inadequate adjustment of the lens of the eye (i.e., loss of accommodation) for various distances, which causes objects that are close to the eye to appear blurry.
In most people, the symptoms of Presbyopia begin to become noticeable under normal viewing conditions at around age 40, or shortly thereafter. However, Presbyopia actually begins to occur before the symptoms become noticeable and increases throughout a person's lifetime. In general, a person is deemed “symptomatic” when the residual accommodation is less than that required for one to read. Typical reading distance requires an accommodation ADD of 2.0 to 3.0 Diopters. Eventually, the residual accommodation is reduced to the point at which the individual becomes an absolute Presbyope after age 50. Symptoms of Presbyopia result in the inability to focus on objects close at hand. As the lens hardens, it is unable to focus the rays of light that come from nearby objects. People that are symptomatic typically have difficulty reading small print, such as that on computer display monitors, in telephone directories and newspaper advertisements, and may need to hold reading materials at arm's length.
There are a variety of non-surgical systems that are currently used to treat Presbyopia, including bifocal spectacles, progressive (no-line bifocal) spectacles, reading spectacles, bifocal contact lenses, and monovision contact lenses. Surgical systems include, for example, multifocal intraocular lenses (IOLs) and accommodation IOLs inserted into the eye and vision systems altered through corneal ablation techniques. Each of these systems has certain advantages and disadvantages relative to the others. With bifocal spectacles, the top portion of the lens serves as the distance lens while the lower portion serves as the near vision lens. Bifocal contact lenses generally work well for patients who have a good tear film (i.e., moist eyes), good binocular vision (i.e., ability to focus both eyes together), good visual accuity (i.e., sharpness) in each eye, and no abnormalities or disease in the eyelids. The bifocal contact lens wearer must invest the time required to maintain contact lenses, and generally should not be involved in occupations that impose high visual demands on the person. Furthermore, bifocal contact lenses may limit binocular vision. In addition, bifocal contact lenses are relatively expensive, in part due to the time it takes the patient to be accurately fitted.
An alternative to spectacles and bifocal contact lenses are monovision contact lenses. With monovision contact lenses, one lens of the pair corrects for near vision and the other corrects for distance vision. For an emmetropic individual, i.e., an individual who does not require distance vision correction, only a single contact lens is worn in one eye to correct for near vision. With non-emmetropic individuals, one of the monovision contact lenses sets the focus of one eye, typically the dominate eye, at distance and the other lens adds a positive power bias to the other eye. The magnitude of the positive power bias depends on the individual's residual accommodation and near vision requirements. Individuals with low ADD requirements typically adapt very well to monovision contact lenses. Advantages of monovision are patient acceptability, convenience, and lower cost. Disadvantages include headaches and fatigue experienced by the wearer during the adjustment period and decreases in visual accuity, which some people find unacceptable. As the ADD difference is increased, a loss of depth perception, night vision and intermediate vision limits its effectiveness of monovision systems.
Simultaneous vision multifocal contact lenses are also used to treat Presbyopia. Types of multifocal contact lenses include, but are not limited to, center distance power designs, center near power designs, annular power designs, diffractive power designs, and the like. Center near power designs are multifocal, or progressive, contact lenses used to treat Presbyopia. These lenses have a near vision zone in the center of the lens that extends outwardly a distance away from the center of the lens and a distance vision zone that is on the periphery of the lens and is concentric with and surrounds the near vision zone. With more modern multifocal contact lenses, known as progressive contact lenses, the transition between the near and distance vision regions is more gradual than in earlier designs. The ADD power is highest in the near vision region of the lens and lowest or zero in the distance vision region of the lens. In the transition region, the power continuously decreases from near vision ADD power to distance vision ADD power (or no ADD power) as the lens transitions from the near vision zone to the distance vision zone.
While multifocal lenses generally are effective at treating symptoms of Presbyopia, there are many disadvantages associated with multifocal lenses. Multifocal lenses designed to treat symptoms of Presbyopia normally have relatively high ADD powers in the near vision zone of the lens to provide the correction needed for near vision. The high ADD power in the near vision zone can result in visual artifacts, or ghost images, that affect the wearer's intermediate vision and can result in other problems that compromise the wearer's distance vision.
Another shortcoming of current Presbyopic treatment systems is that most are ineffective at treating pre-Presbyopia, or emerging Presbyopia. Even prior to the symptoms of Presbyopia becoming readily noticeable to a person, that person may be experiencing pre-Presbyopia symptoms, such as inability of the vision system of the eye to accommodate in conditions of darkness or low lighting. Progressive multifocal lenses with very high near vision ADD powers are not suitable for use to treat pre-Presbyopia. CooperVision, Inc., a company headquartered in Fairport, N.Y., recently began testing a contact lens that it claims is effective at treating pre-Presbyopia, but insufficient information is currently available about this product to verify that the lens is actually effective at treating pre-Presbyopia.
Accordingly, a need exists for a system for treating Presbyopia and pre-Presbyopia that is effective and that does not compromise the wearer's intermediate or distance vision through the stages of Presbyopia.